The present invention relates generally to an apparatus for generating sinusoidal signals of high tonal purity and more particularly to a synthesized sinusoidal generator using a plurality of unity gain switching amplifiers.
In most communication systems, it is commonly necessary to have a source of high power single spectral line with a specified tonal purity to identify the harmonic amplitude limitations. For such a purpose, use of switching amplifiers is considered a logical choice. Since switching amplifiers have a theoretically infinite bandwidth, the spectral requirements must be fulfilled by synthesizing a quasi-sinusoidal wave form which will conform to the harmonic amplitude limitations of the desired single spectral line. The conventional methods develop the synthesized sinusoid by summing a fundamental square wave with its attenuated harmonics. These methods employ circuitry to generate the fundamental as well as the harmonics required thereof by each switching amplifier of the synthesized sinusoidal network. However, the energy contribution from each spectral component is unique. As an example, for an amplitude A for the fundamental of frequency f.sub.1, the third harmonic amplitude would be attenuated to A/3 and the fifth harmonic amplitude to A/5, and so on. Thus such methods do not lend themselves to optimizing the power transfer because of the reduced power requirements of the harmonics. It is thus desirable to have a sinusoid generator where power requirements of the harmonics are not changed.